John mcdonald



(No Model.)

J. MGDONALD. BALANGBD SLIDE VALVE.

No. 477,307. Patented June 2 1, 1892.

UNITED STATES PATENT OFFICE.

JOHN MCDONALD, OF TOKIO, JAPAN.

BALANCED SLIDE-VALVE.

SPECIFICATION forming part of Letters Patent No. 477,307, dated June 21, 1892.

Application filed May 2,1891.

To @ZZ whom, t may concern,.-

Be itknown that l, JOHN MCDONALD, a subject of the Queen of Great Britain, residing at Tokio, Japan, have invented a new and useful Improvement in Balanced Slide-Valves, of which the following is a full, clear, and exact description.

The objectof the invention is to provide a new and improved balanced slide-valve, which is simple and durable in construction, veryeffective in operation, and not liable to get out of order. y

The invention consists of a slide valve formed with an open top and a crown-plate or cover tted to slide in the said slide-valve and adapted to be pressed by back-pressure of the cylinder in contact with the face-plate held on the steam-chest cover.

The invention also consists of certain parts and details and combinations of the same, as will be hereinafter fully described, and then pointed out in the claims.

Reference is to be had to the accompanying drawings, forming a part of this specification, in which similar letters of reference indicate corresponding parts in all the figures.

Figure l is a sectional side elevation of the improvement as applied. Fig. 2 is a transversc section of part of the same. Fig. 3 is a sectional plan view of part of the improvement on the line no m of Fig. 1, and Fig. 4 is a plan View of the air-valve.

The cylinder A,on which the improvement is applied, is provided with the usual inletports d and b and the exhaust-port c,opening into the steam-chest B, in which is fitted to slide a slide-valve C, engaged by a yoke D, carrying the valve-stems E, actuated in the usual manner to impart a reciprocating motion to the said slide-valve. The latter is provided with the usual opening CZ, adapted to alternately connect the ports a and b with the exhaust-portc.

The slide-valve C is open on the top and is formed with sides O', on Which is iitted to slide vertically a crown-plate or cover F, formed at its upper end with aiange F", adapted to be seated against the under side of a face-plate G, secured by suitable means to the underside of the cover H of the steam-chest B.

In the middle of the cover H and base-plate G is arranged a valve I, which opens into the Serial No. 391,337. (No model.)

steam-chest over the yspace covered by the crown-plate or cover F of the slide-valve C. The valve I is provided on its top with openings I, adapted to register with openings J', formed in a disk J, held on a stud K, mounted to turn in the top of the valve I, and carrying on its outer end an arm L, connected with a lever or link N, under the control of the operator, lso that the openings I and J may be brought to register with each other or be disconnected, as desired, and for the purpose vhereinafter more fully described.

l On the inner surface of the side Walls C of the slide-Valve C are fitted packing-strips O, pressed against the outer surface of the crownplate F by live steam in the steam-chest B, the said live steam passing through a recess D in the yoke D into openings C2, formed in the said side walls and leading to the said packing-strips. Similar packing-strips P are held in the outer surface of the crown-plate F, and are pressed in contact with the inner surface of the side walls C by means of springs Q, attached to the under side of the crown-plate and pressing on pins P', connected with the said packing-strips P. The springs Q, as Well as the back-pressure from the cylinder, hold the packing-strips P in firm contact with the side walls, so that no leakage of live steam from the steam-chest B is possible to the interior of the slide-valve C.

The operation is as follows: When 'the engine is started and the valve I is in the position shown in Fig. 1, then the crown-plate F is exposed to atmospheric pressure, and consequently assumes a lowermost position-that is, the top surface of its flange F is disconnected from the under side of the face-plate G. Now when the live steam enters the steamchest B, part of this live steam can escape over the iange F and out of the valve I to the open air. The engine is actuated in the usual manner by the live steam entering the ports a and b alternately, the exhaust'taking place in the usual manner through the port-s b c and a c, respectively. Soon after the engine is started the unbalanced pressure in the chest, acting on the lower side of the projecting flange of the crown-plate or cover F of the slide-valve C, forces the said crownplate upward until its flange F rests against the under side of the face-plate G. The valve IOD is thus counierbalan'ced Without aid of springs. It will be seen that as soon as the crown-plate F slides upward the live steam cannot escape farther through the valve I, and hence the operator can see at a glance that the valve now operates completely balanced. As soon as the live steam is shut off from the steam-chestBin stoppingthe engine, the crown-plate F drops to its former position, so that the steam-chest, by the valve l, is opened to the atmosphere, and all vacuum in the cylinder is thereby destroyed.A i It will be seen that this slide-valve is not liable to get out of order, as its Working does not depend on springs. It will further be seen that the operator can readlysee at any time Whether the valve is Working balanced or unbalanced, according to the escaping or noneescaping steam from the valve. I.

Having thus fully described my invention, I claim as new and desire to secure byLetters Patent-..-

l. The combination, with the y-oke having grooves D', of the baianced valve having a verticallyvsliding cover, a packing-groove provided with packing O, and apertures leading through the sides of the valve to said packing and registering at their outer ends with the yoke-grooves D to admit steam to the packing, substantially as set forth.

2. In a balanced slide-valve, the combina tion,wi th a steam-chest provided with an airvalve, of a slide-valve fitted to slide in the said steam-chest and provided with a sliding crownplate or cover adapted to be seated on the face-plate of the said steam-chest, substantially as shown anddescribed.

3. In a balanced slide-valve, the combination, with an open-top valve, of a crown-plate or cover for the valve, fitted to slide vertically in the said valve, packing-strips held in the outer surface of the crownfplate or cover, pins engaging the packing-strips, and sprn gs secured'to the under side of the cover and engaging said pins, substantially as herein shown and described.

4. In a balanced slide-valve, the combination, with a steanifchest provided with an airvalv-e, of the open-top slide-valve C in the steam-chest, and the crown-plate F, fitted to slide in the valve and provided with the ange F', adapted to be seated on the face-plate of the steanrchest, substantially as described.

The above specification of my invention signed by me this 30th day of March, 1891.

J OHN MCDONALD. Vitnesses:

W. N. WHITNEY, EDWIN DUN. 

